Estimation of rock mass deformation modulus from laboratory experiments in Karun dam

Abstract

Estimation of the deformation modulus of rock mass is one of the most important design parameters in a rock engineering project. This paper presents the results of series of laboratory experiments and in-situ measurements of deformation modulus of intact rock and rock mass in Karun dam in Iran. The study aimed at obtaining a correlation between the field and lab deformation modulus in the studied region. Total number of 51 samples were collected and tested in the technical and soil mechanics laboratory according to ASTM and ISRM standard methods in order to estimate the elastic modulus of the rock. Also, in-situ deformation modulus of rock mass was measured using dilatometer tests. Correlation was developed between the field and lab deformation modulus which allows estimation of this parameter to be made in nearby regions. The detailed lab procedure and the results are presented in this paper. Table 1. Rock mass properties in the study area (TSML, 2009). __________________________________________________ Site __________________________________________________ Azadrood Karoon Karoon Kurdistan Dam III Dam IV (Ahwaz) (Ahwaz) __________________________________________________ Rock Mass Schist Slate Limestone Limestone (Calcite) (Asmari)* Rock Structure Dense Dense Dense Layered Layered Layered With Foliation Scattered Small fractures Tissue Fine Coarse Fine Coarse Fine Coarse Color Darken Gray White, Brown White with White Vein Green Vein Marne layer of Calcite Matrix Weak Sedimentary Sedimentary __________________________________________________ * Asmari is one of the biggest calcinations formations in Iran Table 2.Mechanical properties of rock mass in Karun dam (TSML, 2009) __________________________________________________ Setting Site 1 Site 2 Site 3 __________________________________________________ RQD(%) 79.0 78.0 80.0 RMR (%) 90.0 89.0 98.0 Friction Angles (Degree) 36.6 45.5 56.6 Cohesion Strength (MPa) 2.16 3.54 5.21 Poisson Ratio 0.23 0.22 0.21 Elasticity Modulus (GPa) 4.56 5.01 7.48 Deformation Modulus(GPa)2.10 3.02 5.80 Uniaxial Strength (MPa) 54.0 98.0 121.0 Point Load Test (Mpa) 1.80 2.09 4.18 Ground Condition* RW DMW DMW __________________________________________________ * Ground Condition Definition: RW (Random Weathered), DMW (Dense Moderated Weathered) 3 DILATOMETER IN-SITU TEST In an in-situ dilatometer test the target zone, which is isolated using flexible rubber sleeves, is pressurized using fluid. Constant measurement of the rock mass deformation is made during the pressurization period using three potentiometers or linear variable differential transformers (LVDT) that are installed inside the sleeve and placed with 120° angle with respect to each other (TSML, 2009). Proper arrangement of the LVDTs inside the sleeve is an important aspect in the test in order to obtain reliable results with respect to anisotropic behavior of the rock mass. Series of dilatometer tests were conduced in Karun dam rock mass and the monitored pressure and deformation data transferred and saved into a PC from a data logger with a reading resolution of 15-30 second per data. The Interfels dilatometer (IF096 model) was utilized in this project, a photo of which is shown in Figure 1 and its specifications are tabulated in Table 3. It is to be noted that the dilatometer used in this project is suitable for hard rocks. One may use other types of dilatometer equipped with inflatable volume facility to apply in soft and weathered rocks. When the deformation is determined using volumetric approach, the medium is considered to be isotropic in the test zone. Also, the alteration and weathering zones may affect the results as they reduce the rock strength. (Unal, 1997). Figure 1. The main probe equipment for the dilatometer with 96 mm diameter (TSML, 2009). Table 3. Technical Specifications of Interfels dilatometer (TSML, 2009) __________________________________________________ __________________________________________________ Inflatable packer length 1000 mm Maximum packer pressure 100 bar Maximum Diameter 115 mm Minimum Diameter 95 mm Weight 49 Kg Length (with short protective tube) 1770 mm Length (with long protective tube) 4900 mm The dilatometer test is performed in different loading and unloading cycles, from which several moduli are obtained depending on the application required. The test starts with applying an initial pressure Pi, which increased in four regular steps to a maximum pressure. The increase in platen pressure causes the borehole to widen in its diameter, as shown in Figure 2. In practice the initial pressure, Pi, maybe chosen between 2% and 5% of the maximum pressure. Also, the pressure corresponding to loading steps of 1 and 2 are 33% and 67% of that of in step 3, respectively. The boreholes drilled in order to conduct the dilatometer tests were as deep as 26 m. The borehole diameter widening was recorded during the dilatometer test. Figure 3 shows a photo of the digital recording facilities which transfers the dilatometer reading to a PC.